"French investigators are in the process of investigating our offices," a Lafarge spokeswoman told AFP, confirming a report to that effect by France Inter radio.
"We are cooperating fully with investigators, but we cannot make any further comment on this ongoing inquiry," she said.
A source close to the case said Belgian police were conducting a similar search at the offices of one of Lafarge's subsidiaries in Brussels.
Since June, three French judges have been investigating reported money transfers by Lafarge to groups in Syria, including IS, to keep operations up and running at its Jalabiya cement works in northern Syria in 2013 and 2014, despite the conflict engulfing the country.
The investigation is also seeking to determine whether Lafarge knew of any corresponding financial agreements and whether Syrian employees were put at risk given the precarious security situation.
Lafarge clung on in Syria for two years after most French companies had left as IS made major territorial gains, extending its influence over vast swathes of the country. The group eventually took over the Jalabiya plant in September 2014.
To ensure protection of its staff between 2013 and 2014, Lafarge Cement Syria paid between $80,000 and $100,000 a month to various armed groups, including $20,000 to IS, according to a source close to the year-old investigation first revealed last year by Le Monde daily.
Weeks after the story broke with Le Monde saying Lafarge in Paris knew of the reported arrangements, the French treasury opened an investigation.
'Mistakes in Syria'
Lafarge, which in 2015 merged with Swiss counterpart Holcim, has already admitted to "unacceptable mistakes committed in Syria".
A report by the French national customs judicial department, seen by AFP, has concluded that the company "made payments to jihadist groups" to allow the plant to stay on stream.
The report goes on to say that the firm validated the transactions using false accounting documents.
A statement from Lafarge on Tuesday said the company "strongly condemned the mistakes made in Syria" and had taken measures to ensure the situation cannot be repeated.
The case was treated "with the utmost seriousness at the heart of the company, which in 2016 tasked a law firm to carry out an independent investigation."
Some figures at Lafarge have stated Paris backed the company's determination to retain a foothold in Syria, despite the war, in order to be at the front of the queue for future lucrative reconstruction contracts there.
A senior Lafarge official has told investigators the company had the blessing of the government of the previous Socialist president Francois Hollande to stay on during the fighting.
The anti-corruption association Sherpa, one of 12 civil plaintiffs in the case, has called for former French foreign minister Laurent Fabius to be questioned over the payment.
French examining magistrates have so far questioned several Syrian former employees of the factory.